Look up table with data element promotion

ABSTRACT

Disclosed embodiments relate to look up table operations implemented in a digital data processor. A look up table read instruction recalls data elements of a specified data size from table(s) and stores recalled data elements in successive slots in a destination register. Disclosed embodiments promote data elements to a larger size with selected sign or zero extension. A source operand register stores vector offsets from a table start address. A destination operand stores the results of the look up table read. The look up table instruction implies a base address register and a configuration register. The base address register stores a table base address. The configuration register sets various look up table read operation parameters.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 62/611,395, filed on Dec. 28, 2017, and entitled “LOOK UP TABLE WITH DATA ELEMENT PROMOTION,” which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The technical field of this disclosure is digital data processing and more specifically to improvements in the look up table operations.

BACKGROUND

Modern digital signal processors (DSP) face multiple challenges. Workloads continue to increase, requiring increasing bandwidth. Systems on a chip (SOC) continue to grow in size and complexity. Memory system latency severely impacts certain classes of algorithms. As transistors get smaller, memories and registers become less reliable. As software stacks get larger, the number of potential interactions and errors becomes larger. Even wires become an increasing challenge. Wide busses are difficult to route. Wire speeds continue to lag transistor speeds. Routing congestion is a continual challenge.

One technique useful for filtering functions is table look up. A data table is loaded into memory storing a set of results at a memory location corresponding to an input parameter. To perform a function, the input parameter is used to recall the pre-calculated result. This technique can be particularly valuable for seldom used and difficult to calculate mathematical functions.

SUMMARY

This disclosure relates to look up table operations. The size of the data elements stored in the table may not match the data size needed by the data processor. An algorithm that needs the same table data in two precisions previously required storing and employing two tables. The table to be used was selected based on the needed data size typically wasting memory space. Another problem is the granularity of the look up table. The filtering algorithm may require table values for inputs between the inputs stored.

Disclosed embodiments may be implemented in a digital data processor. An instruction memory stores instruction specifying data processing operations. An instruction decoder sequentially recalls instructions and determines the specified data processing operation and operand(s). An operational unit response to a look up table read instruction is to: recall data elements from at least one table having an instruction specified data size; and store recalled data elements in successive slots in an instruction specified destination register.

Certain disclosed embodiments implement two special purpose look up table read operations. A first special operation promotes the data elements recalled from the table to a larger size. Data element sizes are typically integral powers of two (2^(N)) bits. In one example embodiment, the look up table read instruction supports no promotion, 2× promotion, 4× promotion and 8× promotion. The promotion provides extension bits for each recalled data element. The look up table instruction can treat the data elements as unsigned integers and zero extend the data element into the extension bits. The look up table instruction can treat the data elements as signed integers and sign extend the data element into the extension bits.

The look up table instruction specifies a source operand as register storing a set of vector offsets from a table start address to the accessed data element. The look up table instruction specifies a destination operand as a register storing the results of the look up table read instruction. The look up table instruction implies a look up table base address register and a look up table configuration register. In one embodiment, the look up table read instruction specifies a table set of plural tables from among plural table sets. The look up table base address register and a look up table configuration register are tied to the designated table set. The base address register stores a table base address. Offsets from this base address are derived from the source operand register. The configuration register sets many of the look up table read operation parameters. These parameters include: promotion mode (none, 2×, 4× and 8×); the amount of memory allocated to the corresponding table set (table size); whether the recalled data elements are to be treated as signed integers or unsigned integers; the size of the table data elements; and the number of tables in the table set.

The tables for these look up table read operations may be mapped into level one data cache directly addressable memory in accordance with commonly-assigned U.S. Pat. No. 6,606,686 entitled UNIFIED MEMORY SYSTEM ARCHITECTURE INCLUDING CACHE AND DIRECTLY ADDRESSABLE STATIC RANDOM ACCESS MEMORY, which is incorporated herein by reference. These tables may be loaded by normal memory operations. In one example embodiment, the data processor supports up to 4 separate sets of parallel look up tables. Within a set, up to 16 tables can be looked up in parallel with byte, half word or word element sizes. In accordance with this example embodiment, at least the portion of level one data cache devoted to directly addressed memory has 16 banks. This permits parallel access to 16 memory locations and supports up to 16 tables per table set.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of this invention are illustrated in the drawings, in which:

FIG. 1 illustrates a dual scalar/vector datapath processor according to one embodiment;

FIG. 2 illustrates the registers and functional units in the dual scalar/vector datapath processor illustrated in FIG. 1;

FIG. 3 illustrates a global scalar register file;

FIG. 4 illustrates a local scalar register file shared by arithmetic functional units;

FIG. 5 illustrates a local scalar register file shared by multiply functional units;

FIG. 6 illustrates a local scalar register file shared by load/store units;

FIG. 7 illustrates a global vector register file;

FIG. 8 illustrates a predicate register file;

FIG. 9 illustrates a local vector register file shared by arithmetic functional units;

FIG. 10 illustrates a local vector register file shared by multiply and correlation functional units;

FIG. 11 illustrates pipeline phases of a central processing unit according to an example embodiment;

FIG. 12 illustrates sixteen instructions of a single fetch packet;

FIG. 13 illustrates an instruction coding example in accordance with one embodiment;

FIG. 14 illustrates the bit coding of a condition code extension slot 0;

FIG. 15 illustrates the bit coding of a condition code extension slot 1;

FIG. 16 illustrates the bit coding of a constant extension slot 0;

FIG. 17 is a partial block diagram illustrating constant extension;

FIG. 18 illustrates a carry control for SIMD operations according an example embodiment;

FIG. 19 illustrates the data fields of an example look up table configuration register;

FIG. 20 illustrates the data fields in an example look up table enable register which specifies the type of operations permitted for a particular table set;

FIG. 21 illustrates look up table organization for one table for that table set;

FIG. 22 illustrates look up table organization for two tables for that table set;

FIG. 23 illustrates look up table organization for four tables for that table set;

FIG. 24 illustrates look up table organization for eight tables for that table set;

FIG. 25 illustrates look up table organization for sixteen tables for that table set;

FIG. 26 illustrates an example of the operation of the look up table read instruction for four parallel tables, a data element size of byte and no promotion in accordance with an example embodiment;

FIG. 27 illustrates an example of the operation of the look up table read instruction for four parallel tables, a data element size of byte and 2× promotion in accordance with an example embodiment;

FIG. 28 illustrates an example of the operation of the look up table read instruction for four parallel tables, a data element size of byte and 4× promotion in accordance with an example embodiment;

FIGS. 29A and 29B together illustrate an example embodiment of implementation of the promotion;

FIG. 30 illustrates an example of an extension element illustrated in FIG. 29A; and

FIG. 31 illustrates a multiplex control encoder controlling multiplexers illustrated in FIGS. 29A and 29B.

DETAILED DESCRIPTION

FIG. 1 illustrates a dual scalar/vector datapath processor 100 according to an example embodiment of this disclosure. Processor 100 includes separate level one instruction cache (L1I) 121 and level one data cache (L1D) 123. Processor 100 includes a level two combined instruction/data cache (L2) 130 that holds both instructions and data. FIG. 1 illustrates the connection between level one instruction cache 121 and level two combined instruction/data cache 130 (bus 142). FIG. 1 illustrates the connection between level one data cache 123 and level two combined instruction/data cache 130 (bus 145). The level two combined instruction/data cache 130 stores both instructions to back up level one instruction cache 121 and data to back up level one data cache 123. The level two combined instruction/data cache 130 is further connected to higher level cache and/or main memory in a manner known in the art and not illustrated in FIG. 1. In one embodiment, central processing unit core 110, level one instruction cache 121, level one data cache 123 and level two combined instruction/data cache 130 are formed on a single integrated circuit. This single integrated circuit optionally includes other circuits.

Central processing unit core 110 fetches instructions from level one instruction cache 121 as controlled by instruction fetch unit 111. Instruction fetch unit 111 determines the next instructions to be executed and recalls a fetch packet sized set of such instructions. The nature and size of fetch packets are further detailed below. As known in the art, instructions are directly fetched from level one instruction cache 121 upon a cache hit (if these instructions are stored in level one instruction cache 121). Upon a cache miss (the specified instruction fetch packet is not stored in level one instruction cache 121), these instructions are sought in level two combined cache 130. In one embodiment, the size of a cache line in level one instruction cache 121 equals the size of a fetch packet. The memory locations of these instructions are either a hit in level two combined cache 130 or a miss. A hit is serviced from level two combined cache 130. A miss is serviced from a higher level of cache (not illustrated) or from main memory (not illustrated). As is known in the art, the requested instruction may be simultaneously supplied to both level one instruction cache 121 and central processing unit core 110 to speed use.

Central processing unit core 110 includes plural functional units (also referred to as “execution units”) to perform instruction specified data processing tasks. Instruction dispatch unit 112 determines the target functional unit of each fetched instruction. In one embodiment, central processing unit 110 operates as a very long instruction word (VLIW) processor capable of operating on plural instructions in corresponding functional units simultaneously. A compiler may organize instructions in execute packets that are executed together. Instruction dispatch unit 112 directs each instruction to its target functional unit. In one embodiment, the functional unit assigned to an instruction is completely specified by the instruction produced by a compiler in that the hardware of central processing unit core 110 has no part in this functional unit assignment. Instruction dispatch unit 112 may operate on plural instructions in parallel. The number of such parallel instructions is set by the size of the execute packet. This will be further detailed below.

One part of the dispatch task of instruction dispatch unit 112 is determining whether the instruction is to execute on a functional unit in scalar datapath side A 115 or vector datapath side B 116. An instruction bit within each instruction called the s bit determines which datapath the instruction controls. This will be further detailed below.

Instruction decode unit 113 decodes each instruction in a current execute packet. Decoding includes identification of the functional unit performing the instruction, identification of registers used to supply data for the corresponding data processing operation from among possible register files, and identification of the register destination of the results of the corresponding data processing operation. As further explained below, instructions may include a constant field in place of one register number operand field. The result of this decoding is signals for control of the target functional unit to perform the data processing operation specified by the corresponding instruction on the specified data.

Central processing unit core 110 includes control registers 114. Control registers 114 store information for control of the functional units in scalar datapath side A 115 and vector datapath side B 116. This information could include mode information or the like.

The decoded instructions from instruction decode unit 113 and information stored in control registers 114 are supplied to scalar datapath side A 115 and vector datapath side B 116. As a result, functional units within scalar datapath side A 115 and vector datapath side B 116 perform instruction specified data processing operations upon instruction specified data and store the results in an instruction specified data register or registers. Each of scalar datapath side A 115 and vector datapath side B 116 includes plural functional units that may operate in parallel. These will be further detailed below in conjunction with FIG. 2. There is a datapath 117 between scalar datapath side A 115 and vector datapath side B 116 permitting data exchange.

Central processing unit core 110 includes further non-instruction based modules. Emulation unit 118 permits determination of the machine state of central processing unit core 110 in response to instructions. This capability will typically be employed for algorithmic development. Interrupts/exceptions unit 119 enables central processing unit core 110 to be responsive to external, asynchronous events (interrupts) and to respond to attempts to perform improper operations (exceptions).

Central processing unit core 110 includes streaming engine 125. Streaming engine 125 supplies two data streams from predetermined addresses typically cached in level two combined cache 130 to register files of vector datapath side B. This provides controlled data movement from memory (as cached in level two combined cache 130) directly to functional unit operand inputs. This is further detailed below.

FIG. 1 illustrates data widths of busses between various parts for an example embodiment. Level one instruction cache 121 supplies instructions to the instruction fetch unit 111 via bus 141. Bus 141 is a 512-bit bus in this example embodiment. Bus 141 is unidirectional from level one instruction cache 121 to central processing unit 110. Level two combined cache 130 supplies instructions to level one instruction cache 121 via bus 142. Bus 142 is a 512-bit bus in this example embodiment. Bus 142 is unidirectional from level two combined cache 130 to level one instruction cache 121.

Level one data cache 123 exchanges data with register files in scalar datapath side A 115 via bus 143. Bus 143 is a 64-bit bus in this example embodiment. Level one data cache 123 exchanges data with register files in vector datapath side B 116 via bus 144. Bus 144 is a 512-bit bus in this example embodiment. Busses 143 and 144 are illustrated as bidirectional supporting both central processing unit 110 data reads and data writes. Level one data cache 123 exchanges data with level two combined cache 130 via bus 145. Bus 145 is a 512-bit bus in this example embodiment. Bus 145 is illustrated as bidirectional supporting cache service for both central processing unit 110 data reads and data writes.

As known in the art, CPU data requests are directly fetched from level one data cache 123 upon a cache hit (if the requested data is stored in level one data cache 123). Upon a cache miss (the specified data is not stored in level one data cache 123), this data is sought in level two combined cache 130. The memory locations of this requested data is either a hit in level two combined cache 130 or a miss. A hit is serviced from level two combined cache 130. A miss is serviced from another level of cache (not illustrated) or from main memory (not illustrated). As is known in the art, the requested instruction may be simultaneously supplied to both level one data cache 123 and central processing unit core 110 to speed use.

Level two combined cache 130 supplies data of a first data stream to streaming engine 125 via bus 146. Bus 146 is a 512-bit bus in this example embodiment. Streaming engine 125 supplies data of this first data stream to functional units of vector datapath side B 116 via bus 147. Bus 147 is a 512-bit bus in this example embodiment. Level two combined cache 130 supplies data of a second data stream to streaming engine 125 via bus 148. Bus 148 is a 512-bit bus in this example embodiment. Streaming engine 125 supplies data of this second data stream to functional units of vector datapath side B 116 via bus 149. Bus 149 is a 512-bit bus in this example embodiment. Busses 146, 147, 148 and 149 are illustrated as unidirectional from level two combined cache 130 to streaming engine 125 and to vector datapath side B 116 in accordance with this example embodiment.

Steaming engine data requests are directly fetched from level two combined cache 130 upon a cache hit (if the requested data is stored in level two combined cache 130). Upon a cache miss (the specified data is not stored in level two combined cache 130), this data is sought from another level of cache (not illustrated) or from main memory (not illustrated). In some embodiments, level one data cache 123 may cache data not stored in level two combined cache 130. If such operation is supported, then upon a streaming engine data request that is a miss in level two combined cache 130, level two combined cache 130 may snoop level one data cache 123 for the streaming engine requested data. If level one data cache 123 stores this data, its snoop response would include the data, which is then supplied to service the streaming engine request. If level one data cache 123 does not store this data, its snoop response would indicate this and level two combined cache 130 would then service this streaming engine request from another level of cache (not illustrated) or from main memory (not illustrated).

In one embodiment, both level one data cache 123 and level two combined cache 130 may be configured as selected amounts of cache or directly addressable memory in accordance with the aforementioned U.S. Pat. No. 6,606,686 entitled UNIFIED MEMORY SYSTEM ARCHITECTURE INCLUDING CACHE AND DIRECTLY ADDRESSABLE STATIC RANDOM ACCESS MEMORY.

FIG. 2 illustrates further details of functional units and register files within scalar datapath side A 115 and vector datapath side B 116 in accordance with one example embodiment. Scalar datapath side A 115 includes global scalar register file 211, L1/S1 local register file 212, M1/N1 local register file 213 and D1/D2 local register file 214. Scalar datapath side A 115 includes L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225 and D2 unit 226. Vector datapath side B 116 includes global vector register file 231, L2/S2 local register file 232, M2/N2/C local register file 233 and predicate register file 234. Vector datapath side B 116 includes L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245 and P unit 246. These functional units may be configured to read from or write to certain register files, as will be detailed below.

L1 unit 221 may accept two 64-bit operands and produce one 64-bit result. The two operands are each recalled from an instruction specified register in either global scalar register file 211 or L1/S1 local register file 212. L1 unit 221 may perform the following instruction selected operations: 64-bit add/subtract operations; 32-bit min/max operations; 8-bit Single Instruction Multiple Data (SIMD) instructions such as sum of absolute value, minimum and maximum determinations; circular min/max operations; and various move operations between register files. The result produced by L1 unit 221 may be written into an instruction specified register of global scalar register file 211, L1/S1 local register file 212, M1/N1 local register file 213, or D1/D2 local register file 214.

S1 unit 222 may accept two 64-bit operands and produce one 64-bit result. The two operands are each recalled from an instruction specified register in either global scalar register file 211 or L1/S1 local register file 212. In one embodiment, S1 unit 222 may perform the same type of operations as L1 unit 221. In other embodiments, there may be slight variations between the data processing operations supported by L1 unit 221 and S1 unit 222. The result produced by S1 unit 222 may be written into an instruction specified register of global scalar register file 211, L1/S1 local register file 212, M1/N1 local register file 213, or D1/D2 local register file 214.

M1 unit 223 may accept two 64-bit operands and produce one 64-bit result. The two operands are each recalled from an instruction specified register in either global scalar register file 211 or M1/N1 local register file 213. M1 unit 223 may perform the following instruction selected operations: 8-bit multiply operations; complex dot product operations; 32-bit bit count operations; complex conjugate multiply operations; and bit-wise Logical Operations, moves, adds, and subtracts. The result produced by M1 unit 223 may be written into an instruction specified register of global scalar register file 211, L1/S1 local register file 212, M1/N1 local register file 213, or D1/D2 local register file 214.

N1 unit 224 may accept two 64-bit operands and produce one 64-bit result. The two operands are each recalled from an instruction specified register in either global scalar register file 211 or M1/N1 local register file 213. N1 unit 224 may perform the same type operations as M1 unit 223. There may be certain double operations (called dual issued instructions) that employ both the M1 unit 223 and the N1 unit 224 together. The result produced by N1 unit 224 may be written into an instruction specified register of global scalar register file 211, L1/S1 local register file 212, M1/N1 local register file 213, or D1/D2 local register file 214.

D1 unit 225 and D2 unit 226 may each accept two 64-bit operands and each produce one 64-bit result. D1 unit 225 and D2 unit 226 may perform address calculations and corresponding load and store operations. D1 unit 225 is used for scalar loads and stores of 64 bits. D2 unit 226 is used for vector loads and stores of 512 bits. D1 unit 225 and D2 unit 226 also may perform: swapping, pack and unpack on the load and store data; 64-bit SIMD arithmetic operations; and 64-bit bit-wise logical operations. D1/D2 local register file 214 will generally store base and offset addresses used in address calculations for the corresponding loads and stores. The two operands are each recalled from an instruction specified register in either global scalar register file 211, or D1/D2 local register file 214. The calculated result by D1 unit 225 and/or D2 unit 226 may be written into an instruction specified register of global scalar register file 211, L1/S1 local register file 212, M1/N1 local register file 213, or D1/D2 local register file 214.

L2 unit 221 may accept two 512-bit operands and produce one 512-bit result. Each of up to two operands are each recalled from an instruction specified register in either global vector register file 231, L2/S2 local register file 232 or predicate register file 234. L2 unit 241 may perform instruction similar to L1 unit 221 except on wider 512-bit data. The result produced by L2 unit 241 may be written into an instruction specified register of global vector register file 231, L2/S2 local register file 232, M2/N2/C local register file 233, or predicate register file 234.

S2 unit 242 may accept two 512-bit operands and produce one 512-bit result. Each of up to two operands are each recalled from an instruction specified register in either global vector register file 231, L2/S2 local register file 232 or predicate register file 234. S2 unit 242 may perform instructions similar to S1 unit 222 except on wider 512-bit data. The result produced by S2 unit 242 may be written into an instruction specified register of global vector register file 231, L2/S2 local register file 232, M2/N2/C local register file 233, or predicate register file 234.

M2 unit 243 may accept two 512-bit operands and produce one 512-bit result. The two operands are each recalled from an instruction specified register in either global vector register file 231 or M2/N2/C local register file 233. M2 unit 243 may perform instructions similar to M1 unit 222 except on wider 512-bit data. The result produced by M2 unit 243 may be written into an instruction specified register of global vector register file 231, L2/S2 local register file 232, or M2/N2/C local register file 233.

N2 unit 244 may accept two 512-bit operands and produce one 512-bit result. The two operands are each recalled from an instruction specified register in either global vector register file 231 or M2/N2/C local register file 233. N2 unit 244 may perform the same type operations as M2 unit 243. There may be certain double operations (called dual issued instructions) that employ both M2 unit 243 and the N2 unit 244 together. The result produced by N2 unit 244 may be written into an instruction specified register of global vector register file 231, L2/S2 local register file 232, or M2/N2/C local register file 233.

C unit 245 may accepts two 512-bit operands and produce one 512-bit result. The two operands are each recalled from an instruction specified register in either global vector register file 231 or M2/N2/C local register file 233. C unit 245 may perform: “Rake” and “Search” instructions; up to 512 2-bit PN*8-bit multiplies; I/Q complex multiplies per clock cycle; 8-bit and 16-bit Sum-of-Absolute-Difference (SAD) calculations, up to 512 SADs per clock cycle; horizontal add and horizontal min/max instructions; and vector permutes instructions. In one embodiment, C unit 245 includes 4 vector control registers (CUCR0 to CUCR3) used to control certain operations of C unit 245 instructions. Control registers CUCR0 to CUCR3 are used as operands in certain C unit 245 operations. For example, control registers CUCR0 to CUCR3 may be used in control of a general permutation instruction (VPERM) or as masks for SIMD multiple DOT product operations (DOTPM) and SIMD multiple Sum-of-Absolute-Difference (SAD) operations. Control register CUCR0 may be used to store polynomials for Galois Field Multiply operations (GFMPY). Control register CUCR1 may be used to store a Galois field polynomial generator function.

P unit 246 may perform basic logic operations on registers of local predicate register file 234. P unit 246 has direct access to read from and write to predicate register file 234. The operations performed by P unit 246 may include AND, ANDN, OR, XOR, NOR, BITR, NEG, SET, BITCNT, RMBD, BIT Decimate and Expand. One use of P unit 246 can include manipulation of an SIMD vector comparison result for use in control of a further SIMD vector operation.

FIG. 3 illustrates an example embodiment of global scalar register file 211. In the illustrated embodiment, there are 16 independent 64-bit wide scalar registers designated A0 to A15. Each register of global scalar register file 211 can be read from or written to as 64-bits of scalar data. All scalar datapath side A 115 functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, and D2 unit 226) can read or write to global scalar register file 211. Global scalar register file 211 may be read as 32-bits or as 64-bits and may only be written to as 64-bits. The instruction executing determines the read data size. Vector datapath side B 116 functional units (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246) can read from global scalar register file 211 via crosspath 117 under restrictions that will be detailed below.

FIG. 4 illustrates an example embodiment of D1/D2 local register file 214. In the illustrated embodiment, there are 16 independent 64-bit wide scalar registers designated DO to D16. Each register of D1/D2 local register file 214 can be read from or written to as 64-bits of scalar data. All scalar datapath side A 115 functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, and D2 unit 226) can write to D1/D2 local register file 214. Only D1 unit 225 and D2 unit 226 can read from D1/D1 local register file 214. Data stored in D1/D2 local register file 214 may include base addresses and offset addresses used in address calculations.

FIG. 5 illustrates an example embodiment of L1/S1 local register file 212. The embodiment illustrated in FIG. 5 has 8 independent 64-bit wide scalar registers designated AL0 to AL7. Under certain instruction coding formats (see FIG. 13), L1/S1 local register file 212 can include up to 16 registers. The embodiment of FIG. 5 implements only 8 registers to reduce circuit size and complexity. Each register of L1/S1 local register file 212 can be read from or written to as 64-bits of scalar data. All scalar datapath side A 115 functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, and D2 unit 226) can write to L1/S1 local register file 212. Only L1 unit 221 and S1 unit 222 can read from L1/S1 local register file 212.

FIG. 6 illustrates an example embodiment of M1/N1 local register file 213. The embodiment illustrated in FIG. 6 has 8 independent 64-bit wide scalar registers designated AM0 to AM7. Under certain instruction coding formats (see FIG. 13), M1/N1 local register file 213 can include up to 16 registers. The embodiment of FIG. 6 implements only 8 registers to reduce circuit size and complexity. Each register of M1/N1 local register file 213 can be read from or written to as 64-bits of scalar data. All scalar datapath side A 115 functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, and D2 unit 226) can write to M1/N1 local register file 213. Only M1 unit 223 and N1 unit 224 can read from M1/N1 local register file 213.

FIG. 7 illustrates an example embodiment of global vector register file 231. In the illustrated embodiment, there are 16 independent 512-bit wide vector registers. Each register of global vector register file 231 can be read from or written to as 64-bits of scalar data designated B0 to B15. Each register of global vector register file 231 can be read from or written to as 512-bits of vector data designated VB0 to VB15. The instruction type determines the data size. All vector datapath side B 116 functional units (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246) can read or write to global vector register file 231. Scalar datapath side A 115 functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, and D2 unit 226) can read from global vector register file 231 via crosspath 117 under restrictions that will be detailed below.

FIG. 8 illustrates an example embodiment of P local register file 234. In the illustrated embodiment, there are 8 independent 64-bit wide registers designated P0 to P7. Each register of P local register file 234 can be read from or written to as 64-bits of scalar data. Vector datapath side B 116 functional units L2 unit 241, S2 unit 242, C unit 244, and P unit 246 can write to P local register file 234. Only L2 unit 241, S2 unit 242, and P unit 246 can read from P local register file 234. P local register file 234 may be used for: writing one bit SIMD vector comparison results from L2 unit 241, S2 unit 242, or C unit 244; manipulation of SIMD vector comparison results by P unit 246; and use of the manipulated results in control of a further SIMD vector operation.

FIG. 9 illustrates an example embodiment of L2/S2 local register file 232. The embodiment illustrated in FIG. 9 has 8 independent 512-bit wide vector registers. Under certain instruction coding formats (see FIG. 13), L2/S2 local register file 232 can include up to 16 registers. The embodiment of FIG. 9 implements only 8 registers to reduce circuit size and complexity. Each register of L2/S2 local vector register file 232 can be read from or written to as 64-bits of scalar data designated BL0 to BL7. Each register of L2/S2 local vector register file 232 can be read from or written to as 512-bits of vector data designated VBL0 to VBL7. The instruction type determines the data size. All vector datapath side B 116 functional units (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246) can write to L2/S2 local register file 232. Only L2 unit 241 and S2 unit 242 can read from L2/S2 local vector register file 232.

FIG. 10 illustrates an example embodiment of M2/N2/C local register file 233. The embodiment illustrated in FIG. 10 has 8 independent 512-bit wide vector registers. Under certain instruction coding formats (see FIG. 13), M2/N2/C local register file 233 can include up to 16 registers. The embodiment of FIG. 10 implements only 8 registers to reduce circuit size and complexity. Each register of M2/N2/C local vector register file 233 can be read from or written to as 64-bits of scalar data designated BM0 to BM7. Each register of M2/N2/C local vector register file 233 can be read from or written to as 512-bits of vector data designated VBM0 to VBM7. All vector datapath side B 116 functional units (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246) can write to M2/N2/C local vector register file 233. Only M2 unit 233, N2 unit 244 and C unit 245 can read from M2/N2/C local vector register file 233.

Thus, in accordance with certain disclosed embodiments of this disclosure, global register files may be accessible by all functional units of a side (e.g., scalar and vector) and local register files may be accessible by only some of the functional units of a side. Some additional embodiments in accordance with this disclosure could be practiced employing only one type of register file corresponding to the disclosed global register files.

Crosspath 117 permits limited exchange of data between scalar datapath side A 115 and vector datapath side B 116. During each operational cycle one 64-bit data word can be recalled from global scalar register file 211 for use as an operand by one or more functional units of vector datapath side B 116 and one 64-bit data word can be recalled from global vector register file 231 for use as an operand by one or more functional units of scalar datapath side A 115. Any scalar datapath side A 115 functional unit (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, and D2 unit 226) may read a 64-bit operand from global vector register file 231. This 64-bit operand is the least significant bits of the 512-bit data in the accessed register of global vector register file 231. Scalar datapath side A 115 functional units may employ the same 64-bit crosspath data as an operand during the same operational cycle. However, only one 64-bit operand is transferred from vector datapath side B 116 to scalar datapath side A 115 in any single operational cycle. Any vector datapath side B 116 functional unit (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246) may read a 64-bit operand from global scalar register file 211. If the corresponding instruction is a scalar instruction, the crosspath operand data is treated as any other 64-bit operand. If the corresponding instruction is a vector instruction, the upper 448 bits of the operand are zero filled. Vector datapath side B 116 functional units may employ the same 64-bit crosspath data as an operand during the same operational cycle. Only one 64-bit operand is transferred from scalar datapath side A 115 to vector datapath side B 116 in any single operational cycle.

Streaming engine 125 transfers data in certain circumstances. In the embodiment of FIG. 1, streaming engine 125 controls two data streams. A stream includes a sequence of elements of a particular type. Programs that operate on streams read the data sequentially, operating on each element in turn. Stream data may have the following basic properties: a well-defined beginning and ending time; fixed element size and type throughout the stream; and a fixed sequence of elements. Thus programs cannot seek randomly within the stream. Further, stream data is read-only while active. Thus, programs cannot write to a stream while simultaneously reading from it. Once a stream is opened, streaming engine 125: calculates the address; fetches the defined data type from level two unified cache 130 (which may require cache service from a higher level memory, i.e., in the event of a cache miss in level two unified cache 130); performs data type manipulation (e.g., such as zero extension, sign extension, and/or data element sorting/swapping such as matrix transposition); and delivers the data directly to the programmed data register file within CPU 110. Streaming engine 125 is thus useful for real-time digital filtering operations on well-behaved data. Streaming engine 125 frees these memory fetch tasks from the corresponding CPU 110, thereby enabling the CPU 110 to perform other processing functions.

Streaming engine 125 provides several benefits. For example, streaming engine 125 permits multi-dimensional memory accesses, increases the available bandwidth to functional units of CPU 110, reduces the number of cache miss stalls since the stream buffer bypasses level one data cache 123, reduces the number of scalar operations required to maintain a loop, and manages address pointers. Streaming engine 125 can also handle address generation, which frees up address generation instruction slots and D1 unit 225 and D2 unit 226 for other computations.

CPU 110 operates on an instruction pipeline. Instructions are fetched in instruction packets of a fixed length as further described below. All instructions have the same number of pipeline phases for fetch and decode, but can have a varying number of execute phases.

FIG. 11 illustrates an example embodiment of an instruction pipeline having the following pipeline phases: program fetch phase 1110, dispatch and decode phases 1120, and execution phase 1130. Program fetch phase 1110 includes three stages for all instructions. Dispatch and decode phases 1120 include three stages for all instructions. Execution phase 1130 includes one to four stages dependent on the instruction.

Fetch phase 1110 includes program address generation stage 1111 (PG), program access stage 1112 (PA), and program receive stage 1113 (PR). During program address generation stage 1111 (PG), a program address is generated in the CPU and a read request is sent to a memory controller for the level one instruction cache L1I. During the program access stage 1112 (PA), the level one instruction cache L1I processes the request, accesses the data in its memory, and sends a fetch packet to the CPU boundary. During the program receive stage 1113 (PR), the CPU registers the fetch packet.

In an example embodiment, instructions are fetched as sixteen 32-bit wide slots, constituting a fetch packet, at a time. FIG. 12 illustrates one such embodiment, where a single fetch packet includes sixteen instructions 1201 to 1216. Fetch packets are aligned on 512-bit (16-word) boundaries. The fetch packet, in one embodiment, employs a fixed 32-bit instruction length. Fixed length instructions are advantageous for several reasons. Fixed length instructions enable easy decoder alignment. A properly aligned instruction fetch can load plural instructions into parallel instruction decoders. Such a properly aligned instruction fetch can be achieved by predetermined instruction alignment when stored in memory (fetch packets aligned on 512-bit boundaries) coupled with a fixed instruction packet fetch. An aligned instruction fetch also permits operation of parallel decoders on instruction-sized fetched bits. Variable length instructions may require an initial step of locating each instruction boundary before they can be decoded. A fixed length instruction set generally permits more regular layout of instruction fields. This simplifies the construction of each decoder which is an advantage for a wide issue VLIW central processor.

The execution of the individual instructions is partially controlled by a p bit in each instruction. This p bit can be configured as bit 0 of the 32-bit wide slot. The p bit of an instruction determines whether the instruction executes in parallel with a next instruction. Instructions are scanned from lower to higher addresses. If the p bit of an instruction is 1, then the next following instruction (higher memory address) is executed in parallel with (in the same cycle as) that instruction. If the p bit of an instruction is 0, then the next following instruction is executed in the cycle after the instruction.

CPU 110 and level one instruction cache L1I 121 pipelines are de-coupled from each other. Fetch packet returns from level one instruction cache L1I can take different number of clock cycles, depending on external circumstances such as whether there is a hit in level one instruction cache 121 or a hit in level two combined cache 130. Therefore program access stage 1112 (PA) can take several clock cycles instead of 1 clock cycle as in the other stages.

The instructions executing in parallel constitute an execute packet. In one embodiment, an execute packet can contain up to sixteen instructions (slots). No two instructions in an execute packet may use the same functional unit. A slot can be one of five types: 1) a self-contained instruction executed on one of the functional units of CPU 110 (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, D2 unit 226, L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246); 2) a unitless instruction such as a NOP (no operation) instruction or multiple NOP instructions; 3) a branch instruction; 4) a constant field extension; and 5) a conditional code extension. Some of these slot types will be further explained below.

Dispatch and decode phases 1120 include instruction dispatch to appropriate execution unit stage 1121 (DS), instruction pre-decode stage 1122 (DC1), and instruction decode, operand reads stage 1123 (DC2). During instruction dispatch to appropriate execution unit stage 1121 (DS) the fetch packets are split into execute packets and assigned to the appropriate functional units. During the instruction pre-decode stage 1122 (DC1), the source registers, destination registers, and associated paths are decoded for the execution of the instructions in the functional units. During the instruction decode, operand reads stage 1123 (DC2), more detail unit decodes are done, as well as reading operands from the register files.

Execution phase 1130 includes execution stages 1131 to 1135 (E1 to E5). Different types of instructions may require different numbers of these stages to complete their execution. These stages of the pipeline play an important role in understanding the device state at CPU cycle boundaries.

During execute 1 stage 1131 (E1), the conditions for the instructions are evaluated and operands are operated on. As illustrated in FIG. 11, execute 1 stage 1131 may receive operands from a stream buffer 1141 and one of the register files shown schematically as 1142. For load and store instructions, address generation is performed and address modifications are written to a register file. For branch instructions, a branch fetch packet in PG phase is affected.

As illustrated in FIG. 11, load and store instructions access memory, shown here schematically as memory 1151. For single-cycle instructions, results are written to a destination register file. This assumes that any conditions for the instructions are evaluated as true. If a condition is evaluated as false, the instruction does not write any results or have any pipeline operation after execute 1 stage 1131.

During execute 2 stage 1132 (E2), load instructions send the address to memory. Store instructions send the address and data to memory. Single-cycle instructions that saturate results set a bit (SAT) in the control status register (CSR) if saturation occurs. For 2-cycle instructions, results are written to a destination register file.

During execute 3 stage 1133 (E3), data memory accesses are performed. Any multiply instructions that saturate results set the SAT bit in the control status register (CSR) if saturation occurs. For 3-cycle instructions, results are written to a destination register file

During execute 4 stage 1134 (E4), load instructions bring data to the CPU boundary. For 4-cycle instructions, results are written to a destination register file.

During execute 5 stage 1135 (E5), load instructions write data into a register. This is illustrated schematically in FIG. 11 with input from memory 1151 to execute 5 stage 1135.

FIG. 13 illustrates an instruction coding format 1300 of functional unit instructions in accordance with an example embodiment. Those skilled in the art would realize that other instruction codings are feasible and within the scope of this disclosure. In the illustrated embodiment, each instruction includes 32 bits and controls the operation of one of the individually controllable functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, D2 unit 226, L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246). The bit fields of instruction coding 1300 are defined as follows.

The creg field 1301 (bits 29 to 31) and the z bit 1302 (bit 28) are fields used in conditional instructions. These bits are used for conditional instructions to identify a predicate (also referred to as “conditional”) register and a condition. The z bit 1302 (bit 28) indicates whether the condition is based upon zero or not zero in the predicate register. If z=1, the test is for equality with zero. If z=0, the test is for nonzero. For unconditional instructions, the creg field 1301 and z bit 1302 are set to all Os to allow unconditional instruction execution. The creg field 1301 and the z field 1302 are encoded in the instruction as shown in Table 1.

TABLE 1 Conditional creg z Register 31 30 29 28 Unconditional 0 0 0 0 Reserved 0 0 0 1 A0 0 0 1 z A1 0 1 0 z A2 0 1 1 z A3 1 0 0 z A4 1 0 1 z A5 1 1 0 z Reserved 1 1 x x Execution of a conditional instruction is conditional upon the value stored in the specified conditional data register. In this illustrated example, the conditional register is a data register in the global scalar register file 211. The “z” in the z bit column refers to the zero/not zero comparison selection noted above, and “x” is a do not care state. In this example, the use of three bits for the creg field 1301 in this coding allows for specifying only a subset (A0-A5) of the 16 global registers of global scalar register file 211 as predicate registers. This selection was made to preserve bits in the instruction coding and reduce opcode space.

The dst field 1303 (bits 23 to 27) specifies a register in a corresponding register file as the destination of the instruction results (e.g., where the results are to be written).

The src2/cst field 1304 (bits 18 to 22) can be interpreted in different ways depending on the instruction opcode field (bits 4 to 12 for all instructions and additionally bits 28 to 31 for unconditional instructions). The src2/cst field 1304 indicates a second source operand, either from a register of a corresponding register file or as a constant depending on the instruction opcode field. Depending on the instruction type, when the second source operand is a constant, this may be treated as an unsigned integer and zero extended to a specified data length or may be treated as a signed integer and sign extended to the specified data length.

The src1 field 1305 (bits 13 to 17) specifies a register in a corresponding register file as a first source operand.

The opcode field 1306 (bits 4 to 12) for all instructions (and additionally bits 28 to 31 for unconditional instructions) specifies the type of instruction and designates appropriate instruction options. This includes designation of the functional unit used and the operation performed. Additional details regarding such instruction options are detailed below.

The e bit 1307 (bit 2) is used for immediate constant instructions where the constant may be extended. If e=1, then the immediate constant is extended in a manner detailed below. If e=0, then the immediate constant is not extended. In the latter case, the immediate constant is specified by the src2/cst field 1304 (bits 18 to 22). The e bit 1307 may be used for only some types of instructions. Accordingly, with proper coding, the e bit 1307 may be omitted from instructions which do not need it, and this bit can instead be used as an additional opcode bit.

The s bit 1308 (bit 1) designates scalar datapath side A 115 or vector datapath side B 116. If s=0, then scalar datapath side A 115 is selected, and the available functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225, and D2 unit 226) and register files (global scalar register file 211, L1/S1 local register file 212, M1/N1 local register file 213, and D1/D2 local register file 214) will be those corresponding to scalar datapath side A 115 as illustrated in FIG. 2. Similarly, s=1 selects vector datapath side B 116, and the available functional units (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245, and P unit 246) and register files (global vector register file 231, L2/S2 local register file 232, M2/N2/C local register file 233, and predicate local register file 234) will be those corresponding to vector datapath side B 116 as illustrated in FIG. 2.

The p bit 1308 (bit 0) is used to determine whether the instruction executes in parallel with the following instruction. The p-bits are scanned from lower to higher addresses. If p=1 for the current instruction, then the next instruction executes in parallel with the current instruction. If p=0 for the current instruction, then the next instruction executes in the cycle after the current instruction. All instructions executing in parallel constitute an execute packet. In one example embodiment, an execute packet can contain up to twelve instructions for parallel execution, with each instruction in an execute packet assigned to a different functional unit.

In one example embodiment of processor 100, there are two different condition code extension slots (slot 0 and slot 1). The condition code extension slots may be 32-bit in this example embodiment, as with the coding format 1300 described in FIG. 13. Each execute packet can contain one each of these 32-bit condition code extension slots, which contains the 4-bit creg/z fields (e.g., similar to bits 28 to 31 of coding 1300) for the instructions in the same execute packet. FIG. 14 illustrates an example coding for condition code extension slot 0 and FIG. 15 illustrates an example coding for condition code extension slot 1.

FIG. 14 illustrates an example coding 1400 for condition code extension slot 0. Field 1401 (bits 28 to 31) specify 4 creg/z bits assigned to the L1 unit 221 instruction in the same execute packet. Field 1402 (bits 27 to 24) specify 4 creg/z bits assigned to the L2 unit 241 instruction in the same execute packet. Field 1403 (bits 19 to 23) specify 4 creg/z bits assigned to the S1 unit 222 instruction in the same execute packet. Field 1404 (bits 16 to 19) specify 4 creg/z bits assigned to the S2 unit 242 instruction in the same execute packet. Field 1405 (bits 12 to 15) specify 4 creg/z bits assigned to the D1 unit 225 instruction in the same execute packet. Field 1406 (bits 8 to 11) specify 4 creg/z bits assigned to the D2 unit 226 instruction in the same execute packet. Field 1407 (bits 6 and 7) is unused/reserved. Field 1408 (bits 0 to 5) is coded with a set of unique bits (CCEXO) to identify the condition code extension slot 0. Once this unique ID of condition code extension slot 0 is detected, the corresponding creg/z bits are employed to control conditional execution of any L1 unit 221, L2 unit 241, S1 unit 222, S2 unit 242, D1 unit 224, and D2 unit 225 instructions in the same execution packet. These creg/z bits are interpreted as shown in Table 1. If the corresponding instruction is conditional (e.g., creg/z bits are not all 0) the corresponding bits in the condition code extension slot 0 override the condition code bits (bits 28 to 31 of creg field 1301 and z bit 1302) in the instruction (e.g., coded using coding format 1300). In the illustrated example, no execution packet can have more than one instruction directed to a particular execution unit, and no execute packet of instructions can contain more than one condition code extension slot 0. Thus, the mapping of creg/z bits to functional unit instructions is unambiguous. As discussed above, setting the creg/z bits equal to “0000” makes the instruction unconditional. Thus, a properly coded condition code extension slot 0 can make some corresponding instructions conditional and some unconditional.

FIG. 15 illustrates an example coding 1500 for condition code extension slot 1. Field 1501 (bits 28 to 31) specify 4 creg/z bits assigned to the M1 unit 223 instruction in the same execute packet. Field 1502 (bits 27 to 24) specify 4 creg/z bits assigned to the M2 unit 243 instruction in the same execute packet. Field 1503 (bits 19 to 23) specify 4 creg/z bits assigned to the C unit 245 instruction in the same execute packet. Field 1504 (bits 16 to 19) specify 4 creg/z bits assigned to the N1 unit 224 instruction in the same execute packet. Field 1505 (bits 12 to 15) specify 4 creg/z bits assigned to the N2 unit 244 instruction in the same execute packet. Field 1506 (bits 5 to 11) is unused/reserved. Field 1507 (bits 0 to 5) is coded with a set of unique bits (CCEX1) to identify the condition code extension slot 1. Once this unique ID of condition code extension slot 1 is detected, the corresponding creg/z bits are employed to control conditional execution of any M1 unit 223, M2 unit 243, C unit 245, N1 unit 224 and N2 unit 244 instructions in the same execution packet. These creg/z bits are interpreted as shown in Table 1. If the corresponding instruction is conditional (e.g., creg/z bits are not all 0) the corresponding bits in the condition code extension slot 1 override the condition code bits (bits 28 to 31 of creg field 1301 and z bit 1302) in the instruction (e.g., coded using coding format 1300). In the illustrated example, no execution packet can have more than one instruction directed to a particular execution unit, and no execute packet of instructions can contain more than one condition code extension slot 1. Thus, the mapping of creg/z bits to functional unit instruction is unambiguous. As discussed above, setting the creg/z bits equal to “0000” makes the instruction unconditional. Thus, a properly coded condition code extension slot 1 can make some instructions conditional and some unconditional.

Both condition code extension slot 0 1400 and condition code extension slot 1 may include a p bit to define an execute packet as described above in conjunction with FIG. 13. In one example embodiment, as illustrated in FIGS. 14 and 15, bit 0 of code extension slot 0 1400 and condition code extension slot 1 1500 may provide the p bit. Assuming the p bit for the code extension slots 1400, 1500 is always encoded as 1 (parallel execution), neither code extension slot 1400, 1500 should be the last instruction slot of an execute packet.

In one example embodiment of processor 100, there are two different constant extension slots. Each execute packet can contain one each of these unique 32-bit constant extension slots which contains 27 bits to be concatenated as high order bits with a 5-bit constant field in the instruction coding 1300 to form a 32-bit constant. As noted in the instruction coding 1300 description above, only some instructions define the 5-bit src2/cst field 1304 as a constant rather than a source register identifier. At least some of those instructions may employ a constant extension slot to extend this constant to 32 bits.

FIG. 16 illustrates an example coding 1600 of constant extension slot 0. Each execute packet may include one instance of constant extension slot 0 and one instance of constant extension slot 1. FIG. 16 illustrates that constant extension slot 0 1600 includes two fields. Field 1601 (bits 5 to 31) constitute the most significant 27 bits of an extended 32-bit constant with the target instruction scr2/cst field 1304 providing the five least significant bits. Field 1602 (bits 0 to 4) are coded a set of unique bits (CSTXO) to identify the constant extension slot 0. In an exmaple embodiment constant extension slot 0 1600 is used to extend the constant of one of an L1 unit 221 instruction, data in a D1 unit 225 instruction, an S2 unit 242 instruction, an offset in a D2 unit 226 instruction, an M2 unit 243 instruction, an N2 unit 244 instruction, a branch instruction, or a C unit 245 instruction in the same execute packet. Constant extension slot 1 is similar to constant extension slot 0 except that bits 0 to 4 are coded a set of unique bits (CSTX1) to identify the constant extension slot 1. In an example embodiment, constant extension slot 1 is used to extend the constant of one of an L2 unit 241 instruction, data in a D2 unit 226 instruction, an S1 unit 222 instruction, an offset in a D1 unit 225 instruction, an M1 unit 223 instruction, or an N1 unit 224 instruction in the same execute packet.

Constant extension slot 0 and constant extension slot 1 are used as follows. The target instruction must be of the type permitting constant specification. As known in the art this is implemented by replacing one input operand register specification field with the least significant bits of the constant as described above with respect to scr2/cst field 1304. Instruction decoder 113 determines this case, known as an immediate field, from the instruction opcode bits. The target instruction also includes one constant extension bit (e bit 1307) dedicated to signaling whether the specified constant is not extended (e.g., constant extension bit=0) or the constant is extended (e.g., constant extension bit=1). If instruction decoder 113 detects a constant extension slot 0 or a constant extension slot 1, it further checks the other instructions within that execute packet for an instruction corresponding to the detected constant extension slot. A constant extension is made when a corresponding instruction has a constant extension bit (e bit 1307) equal to 1.

FIG. 17 is a block diagram 1700 illustrating constant extension logic that may be implemented in processor 100. FIG. 17 assumes that instruction decoder 113 detects a constant extension slot and a corresponding instruction in the same execute packet. Instruction decoder 113 supplies the 27 extension bits from the constant extension slot (bit field 1601) and the 5 constant bits (bit field 1304) from the corresponding instruction to concatenator 1701. Concatenator 1701 forms a single 32-bit word from these two parts. In the illustrated embodiment, the 27 extension bits from the constant extension slot (bit field 1601) are the most significant bits and the 5 constant bits (bit field 1305) are the least significant bits. This combined 32-bit word is supplied to one input of multiplexer 1702. The 5 constant bits from the corresponding instruction field 1305 supply a second input to multiplexer 1702. Selection of multiplexer 1702 is controlled by the status of the constant extension bit. If the constant extension bit (e bit 1307) is 1 (extended), multiplexer 1702 selects the concatenated 32-bit input. If the constant extension bit is 0 (not extended), multiplexer 1702 selects the 5 constant bits from the corresponding instruction field 1305. Multiplexer 1702 supplies this output to an input of sign extension unit 1703.

Sign extension unit 1703 forms the final operand value from the input from multiplexer 1703. Sign extension unit 1703 receives control inputs Scalar/Vector and Data Size. The Scalar/Vector input indicates whether the corresponding instruction is a scalar instruction or a vector instruction. The functional units of data path side A 115 (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225 and D2 unit 226) are, in this embodiment, limited to performing scalar instructions. Any instruction directed to one of these functional units is a scalar instruction. Data path side B functional units L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244 and C unit 245 may perform scalar instructions or vector instructions. Instruction decoder 113 determines whether the instruction is a scalar instruction or a vector instruction from the opcode bits. P unit 246 may only perform scalar instructions in this embodiment. The Data Size may be 8 bits (byte B), 16 bits (half-word H), 32 bits (word W), 64 bits (double word D), quad word (128 bit) data or half vector (256 bit) data.

Table 2 lists the operation of sign extension unit 1703 for the various options.

TABLE 2 Instruction Operand Constant Type Size Length Action Scalar B/H/W/D  5 bits Sign extend to 64 bits Scalar B/H/W/D 32 bits Sign extend to 64 bits Vector B/H/W/D  5 bits Sign extend to operand size and replicate across the whole vector Vector B/H/W 32 bits Replicate 32-bit constant across each 32-bit (W) lane Vector D 32 bits Sign extend to 64 bits and replicate across each 64-bit (D) lane

Both constant extension slot 0 and constant extension slot 1 may include a p bit to define an execute packet as described above in conjunction with FIG. 13. In one example embodiment, as in the case of the condition code extension slots, bit 0 of constant extension slot 0 and constant extension slot 1 may provide the p bit. Assuming the p bit for constant extension slot 0 and constant extension slot 1 is always encoded as 1 (parallel execution), neither constant extension slot 0 nor constant extension slot 1 should be in the last instruction slot of an execute packet.

In some embodiments, an execute packet can include a constant extension slot 0 or 1 and more than one corresponding instruction marked constant extended (e bit=1). For constant extension slot 0, this would mean more than one of an L1 unit 221 instruction, data in a D1 unit 225 instruction, an S2 unit 242 instruction, an offset in a D2 unit 226 instruction, an M2 unit 243 instruction, or an N2 unit 244 instruction in an execute packet have an e bit of 1. For constant extension slot 1 this would mean more than one of an L2 unit 241 instruction, data in a D2 unit 226 instruction, an S1 unit 222 instruction, an offset in a D1 unit 225 instruction, an M1 unit 223 instruction or an N1 unit 224 instruction in an execute packet have an e bit of 1. In such instances, instruction decoder 113 may, in one embodiment, determine this case an invalid and unsupported operation. In another embodiment, this combination may be supported with extension bits of the constant extension slot applied to each corresponding functional unit instruction marked constant extended.

Special vector predicate instructions use registers in predicate register file 234 to control vector operations. In the current embodiment, all the SIMD vector predicate instructions operate on selected data sizes. The data sizes may include byte (8 bit) data, half word (16 bit) data, word (32 bit) data, double word (64 bit) data, quad word (128 bit) data and half vector (256 bit) data. Each bit of the predicate register controls whether a SIMD operation is performed upon the corresponding byte of data. The operations of P unit 246 permit a variety of compound vector SIMD operations based upon more than one vector comparison. For example, a range determination can be made using two comparisons. A candidate vector is compared with a first vector reference having the minimum of the range packed within a first data register. A second comparison of the candidate vector is made with a second reference vector having the maximum of the range packed within a second data register. Logical combinations of the two resulting predicate registers would permit a vector conditional operation to determine whether each data part of the candidate vector is within range or out of range.

L1 unit 221, S1 unit 222, L2 unit 241, S2 unit 242 and C unit 245 often operate in a single instruction multiple data (SIMD) mode. In this SIMD mode, the same instruction is applied to packed data from the two operands. Each operand holds plural data elements disposed in predetermined slots. SIMD operation is enabled by carry control at the data boundaries. Such carry control enables operations on varying data widths.

FIG. 18 illustrates the carry control. AND gate 1801 receives the carry output of bit N within the operand wide arithmetic logic unit (64 bits for scalar datapath side A 115 functional units and 512 bits for vector datapath side B 116 functional units). AND gate 1801 also receives a carry control signal which will be further explained below. The output of AND gate 1801 is supplied to the carry input of bit N+1 of the operand wide arithmetic logic unit. AND gates such as AND gate 1801 are disposed between every pair of bits at a possible data boundary. For example, for 8-bit data, such an AND gate will be between bits 7 and 8, bits 15 and 16, bits 23 and 24, etc. Each such AND gate receives a corresponding carry control signal. If the data size is of the minimum, then each carry control signal is 0, effectively blocking carry transmission between the adjacent bits. The corresponding carry control signal is 1 if the selected data size requires both arithmetic logic unit sections. Table 3 below shows example carry control signals for the case of a 512-bit wide operand, such as used by vector datapath side B 116 functional units, which may be divided into sections of 8 bits, 16 bits, 32 bits, 64 bits, 128 bits, or 256 bits. In Table 3 the upper 32 bits control the upper bits (bits 128 to 511) carries and the lower 32 bits control the lower bits (bits 0 to 127) carries. No control of the carry output of the most significant bit is needed, thus only 63 carry control signals are required.

TABLE 3 Data Size Carry Control Signals  8 bits (B) -000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000  16 bits (H) -101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101  32 bits (W) -111 0111 0111 0111 0111 0111 0111 0111 0111 0111 0111 0111 0111 0111 0111 0111  64 bits (D) -111 1111 0111 1111 0111 1111 0111 1111 0111 1111 0111 1111 0111 1111 0111 1111 128 bits -111 1111 1111 1111 0111 1111 1111 1111 0111 1111 1111 1111 0111 1111 1111 1111 256 bits -111 1111 1111 1111 1111 1111 1111 1111 0111 1111 1111 1111 1111 1111 1111 1111 It is typical in the art to operate on data sizes that are integral powers of 2 (2^(N)). However, this carry control technique is not limited to integral powers of 2. One skilled in the art would understand how to apply this technique to other data sizes and other operand widths.

Processor 100 includes dedicated instructions to perform table look up operations implemented via one of D1 unit 225 or D2 unit 226. The tables for these table look up operations are mapped into level one data cache 123 directly addressable memory. An example of such a table/cache configuration is disclosed in accordance with U.S. Pat. No. 6,606,686 entitled UNIFIED MEMORY SYSTEM ARCHITECTURE INCLUDING CACHE AND DIRECTLY ADDRESSABLE STATIC RANDOM ACCESS MEMORY. These tables may be loaded by normal memory operations, such as via a direct memory access (DMA) port, by a special purpose LUTINIT instruction (described below), or just a normal store instruction to the memory space containing the tables. In one example embodiment, processor 100 supports up to 4 separate sets of parallel look up tables and, within a set, up to 16 tables can be looked up in parallel with byte, half word or word element sizes. In accordance with this embodiment, at least the portion of level one data cache 123 devoted to directly addressed memory has 16 banks. This permits parallel access to 16 memory locations and supports up to 16 tables per table set.

These look up tables are accessed with independently specified base and index addresses. A look up table base address register (LTBR) specifies the base address for each set of parallel tables. Each look up table instruction contains a set number identifying which base address register to use for that instruction. Based upon the use of a directly addressable portion of the level one data cache 123, each base address should align with the cache line size of the level one data cache 123. In one embodiment, the cache line size may be 128 bytes.

A look up table configuration register for each set of parallel tables sets controls information to the corresponding set of tables. FIG. 19 illustrates the data fields of an example look up table configuration register 1900. Promotion field 1901 (bits 24 and 25) sets the type of promotion upon storage of elements into a vector register. Promotion field 1901 is decoded as shown in Table 4.

TABLE 4 PROMOTION Description 00 no promotion 01 2x Promotion 10 4x Promotion 11 8x Promotion A field 1901 coding of 00 designates no promotion. A field 1901 coding of 01 designates a 2× promotion. A field 1901 coding of 10 designates a 4× promotion. A field 1901 coding of 11 designates an 8× promotion. In one example embodiment, the promoted data is limited to data sizes up to a double-word size (64 bits). Thus, in such an embodiment: a 2× promotion is valid for a data element size of byte (promoted from byte (8 bits) to half word (16 bits), half word (promoted from half word (16 bits) to word (32 bits), and word (promoted from word (32 bits) to double-word (64 bits); a 4× promotion is valid for a data element size of byte (promoted from byte (8 bit) to word (32 bit) and half word (promoted from half word (16 bit) to double-word (64 bit); and an 8× promotion is only valid for a data element size of byte (promoted from byte (8 bit) to double-word (64 bit). Promotion will be further explained below.

Table size field 1902 (bits 16 to 23) sets the table size. Table Size field 1902 is decoded as shown in Table 5.

TABLE 5 Table Size Size 0000 0000 0.0 Kbytes 0000 0001 1.0 Kbytes 0000 0010 2.0 Kbytes 0000 0011 4.0 Kbytes 0000 0100 8.0 Kbytes 0000 0101 16.0 Kbytes  0000 0110 32.0 Kbytes  0000 0111-1111 reserved 1111 The table base address stored in the corresponding look up table base address register must be aligned to the table size specified in the look up table configuration register.

Signed field 1903 (bit 6) indicates whether processor 100 treats the recalled look up table elements as signed integers or unsigned integers. If the signed field 1903 is 1, processor 100 treats the look up table elements as signed integers. If the signed field 1903 is 0, processor 100 treats the look up table elements as unsigned integers.

Element Size (ESIZE) field 1904 (bits 3 to 5) indicate the look table element size. Element Size field 1904 is decoded as shown in Table 6.

TABLE 6 ELEMENT SIZE Description 000 byte/8 bits 001 half word/16 bits 010 word/32 bits 011-111 reserved

Number of Tables (NTBL) field 1905 (bits 0 to 2) indicates the number of tables to be looked up in parallel. Number of Tables field 1905 is decoded as shown in Table 7.

TABLE 7 NUMBER OF TABLES Description 000  1 table 001  2 tables 010  4 tables 011  8 tables 100 16 tables 101-111 reserved

A look up table enable register 2000 specifies the type of operations permitted for a particular table set. This is illustrated in FIG. 20. As shown in FIG. 20, this example employs a field in a single register to control a corresponding one of the four table sets. Field 2001 controls table set 3. Field 2002 controls table set 2. Field 2003 controls table set 1. Field 2004 controls table set 0. Table Enable fields 2001, 2002, 2003 and 2004 are each decoded as shown in Table 8.

TABLE 8 TABLE ENABLE Description 00 no look up table operations 01 read operations allowed 10 reserved 11 read and write operations allowed If the table set field is 01, then read operations are permitted from the corresponding look up table base address register and the corresponding look up table configuration register. If the table set field is 11, then read operations are permitted from and write operations are permitted to the corresponding look up table base address register and the corresponding look up table configuration register. If the table set field is 00, then no look up table operations are permitted.

Each look up table instruction specifies a vector register as an operand. This vector register is treated as a set of 32-bit look up table indices by the look up table operation corresponding to the instruction. Table 9 shows the coding of the vector indices in the vector operand register based upon the number tables for the set of tables controlled by Number of Tables field 1906 of the corresponding look up table configuration register.

TABLE 9 Vector Register 1 2 4 8 16 bits Index Table Tables tables tables tables Vx[31:0] index0 valid valid valid valid valid Vx[63:32] index1 — valid valid valid valid Vx[95:64] index2 — — valid valid valid Vx[127:96] index3 — — valid valid valid Vx[159:128] index4 — — — valid valid Vx[191:160] index5 — — — valid valid Vx[223:192] index6 — — — valid valid Vx[255:224] index7 — — — valid valid Vx[287:256] index8 — — — — valid Vx[319:288] index9 — — — — valid Vx[351:320] index10 — — — — valid Vx[383:352] index11 — — — — valid Vx[415:384] index12 — — — — valid Vx[447:416] index13 — — — — valid Vx[479:448] index14 — — — — valid Vx[511:480] index15 — — — — valid Depending upon the number of tables specified in the Number of Tables field 1906 of the corresponding look up table configuration register 1900, the vector register bits specify various indices. The address for a table element within the first table for look up table operation is the base address stored in the base address register plus the index specified by bits 0 to 31 of the vector register values. The address for a table element within the second table for look up table operation (assuming at least two tables are specified by number of tables field 1906) is the base address stored in the base address register plus the index specified by bits 32 to 63 of the vector register. Similarly, the vector register specifies an offset for each table specified.

Below is the form of a look up table read (LUTRD) instruction in accordance with one example embodiment.

LUTDR tbl_index, tbl_set, dst

Tbl_index is an instruction operand specifying a vector register (such as within general vector register file 231) by register number. This is interpreted as index numbers as shown in Table 9. Tbl_set is a number [0:3] specifying the table set employed in the instruction. This named table set number specifies: a corresponding look up table base address register storing the table base address, which may a scalar register or a vector register; a corresponding look up table configuration register (FIG. 19), which may a scalar register or a vector register; and the corresponding operative portion of the look up table enable register (FIG. 20), which may a scalar register or a vector register. The look up table base address register corresponding to the named table set determines the base address of the table set. The indices of the vector register named by Tbl_index are offset from this table set base address. The look up table configuration register corresponding to the named table set determines: the promotion mode (Table 4); the amount of memory allocated to the table size (Table 5); the data element size (Table 6); and the number of tables in the table set. Dst is an instruction operand specifying a vector register (such as within general vector register file 231) by register number as the destination of the table look up operation. The data recalled from the table as specified by these other parameters is packed and stored in this destination register. The process of promotion does not add any performance penalty.

FIG. 21 illustrates look up table organization when the corresponding look up table configuration register 1900 specifies one table for that table set. Level one data cache 123 includes a portion of directly addressable memory, including portion 2111 below the look up table, the look up table, and a portion 2112 above the look up table. The corresponding look up table set base address register 2101 specifies the beginning of the table set. In the example of FIG. 21, the number of tables field 1905 specifies a single table. The end of the memory allocated to the table set is specified by the table size field 1902. Index source register 2102 specifies a single offset (index iA) used to address the table. As shown in FIG. 21, the single table employs all 16 banks of memory.

FIG. 22 illustrates look up table organization when the corresponding look up table configuration register 1900 specifies two tables for that table set. The look up table set base address register 2101 specifies the beginning of the table set. The number of tables field 1905 specifies two tables. The end of the memory allocated to the table set is specified by the table size field 1902. Index source register 2102 specifies two offsets used to address the tables. A first index iA addresses Table 1 and a second index iB addresses Table 2. Table 1 data is stored in memory banks 1 to 8. Table 2 data is stored in memory banks 9 to 16.

FIG. 23 illustrates look up table organization when the corresponding look up table configuration register 1900 specifies four tables for that table set. The look up table set base address register 2101 specifies the beginning of the table set. The number of tables field 1905 specifies four tables. The end of the memory allocated to the table set is specified by the table size field 1902. Index source register 2102 specifies four offsets used to address the tables. A first index iA addresses Table 1, a second index iB addresses Table 2, a third index iC addresses Table 3 and a fourth index iD addresses Table 4. Table 1 data is stored in memory banks 1 to 4. Table 2 data is stored in memory banks 5 to 8. Table 3 data is stored in memory banks 9 to 12. Table 4 data is stored in memory banks 13 to 16.

FIG. 24 illustrates look up table organization when the corresponding look up table configuration register 1900 specifies eight tables for that table set. The look up table set base address register 2101 specifies the beginning of the table set. The number of tables field 1905 specifies eight tables. The end of the memory allocated to the table set is specified by the table size field 1902. Index source register 2102 specifies a eight offsets used to address the tables. A first index iA addresses Table 1, a second index iB addresses Table 2, a third index iC addresses Table 3, a fourth index iD addresses Table 4, a fifth index iE addresses Table 5, a sixth index iF addresses Table 6, a seventh index iG addresses Table 7, and an eighth index iH addresses Table 8. Table 1 data is stored in memory banks 1 and 2. Table 2 data is stored in memory banks 3 and 4. Table 3 data is stored in memory banks 5 and 6. Table 4 data is stored in memory banks 7 and 8. Table 5 data is stored in memory banks 9 and 10. Table 6 data is stored in memory banks 11 and 12. Table 7 data is stored in memory banks 13 and 14. Table 8 data is stored in memory banks 15 and 16.

FIG. 25 illustrates look up table organization when the corresponding look up table configuration register 1900 specifies sixteen tables for that table set. The look up table set base address register 2101 specifies the beginning of the table set. The number of tables field 1905 specifies sixteen tables. The end of the memory allocated to the table set is specified by the table size field 1902. Index source register 2102 specifies sixteen offsets used to address the tables. A first index iA addresses Table 1, a second index iB addresses Table 2, a third index iC addresses Table 3, a fourth index iD addresses Table 4, a fifth index iE addresses Table 5, a sixth index iF addresses Table 6, a seventh index iG addresses Table 7, an eighth index iH addresses Table 8, a nineth index iI addresses Table 9, a tenth index iJ addresses Table 10, an eleventh index iK addresses Table 11, a twelveth index iL addresses Table 12, a thirteenth index iM addresses Table 13, a fourteenth index iN addresses Table 14, a fifteenth index iO addresses Table 15, and a sixteenth index iP addresses Table 16. Table 1 data is stored in memory bank 1. Table 2 data is stored in memory bank 2. Table 3 data is stored in memory bank 3. Table 4 data is stored in memory bank 4. Table 5 data is stored in memory bank 5. Table 6 data is stored in memory bank 6. Table 7 data is stored in memory bank 7. Table 8 data is stored in memory bank 8. Table 9 data is stored in memory bank 9. Table 10 data is stored in memory bank 10. Table 11 data is stored in memory bank 11. Table 12 data is stored in memory bank 12. Table 13 data is stored in memory bank 13. Table 14 data is stored in memory bank 14. Table 15 data is stored in memory bank 15. Table 16 data is stored in memory bank 16.

FIG. 26 illustrates an example of the operation of the look up table read instruction of this invention. In the example illustrated in FIG. 26, the corresponding look up table configuration register (1900) specifies four parallel tables, a data element size of byte (8 bits), and no promotion. To perform look up table operations, the look up table enable register field (in register 2000) corresponding to the selected table set must enable either read operation (01) or both read and write operations (11).

The look up table base address register 2101 corresponding to the specified table set stores the base address for the look up table set as illustrated schematically in FIG. 26. The table data is stored in a portion of level one data cache 123 configured as directly accessible memory, such as disclosed in U.S. Pat. No. 6,606,686 entitled UNIFIED MEMORY SYSTEM ARCHITECTURE INCLUDING CACHE AND DIRECTLY ADDRESSABLE STATIC RANDOM ACCESS MEMORY.

The example illustrated in FIG. 26 has four tables: table 1 2611; table 2 2612; table 3 2613; and table 4 2614. As shown in Table 9, this instruction with these selected options treats the data stored in vector source index register 2102 as a set of 4 32-bit fields specifying table offsets. The first field (bits Vx[31:0]) stores iA, the index into the first table 2611. In this example, this indexes to element A5. The second field (bits Vx[63:32]) stores iB, the index into the second table 2612. In this example, this indexes to element B1. The third field (bits Vx[95:64]) stores iC, the index into the third table 2613. In this example, this indexes to element C8. The fourth field (bits Vx[127:96]) stores iD, the index into the fourth table 2611. In this example, this indexes to element D10. The various indices are the memory address offsets from the base address for the table set to the specified data element. In accordance with the operation of this look up table read instruction, the indexed data element in table 1 2611 (A5) is stored in a first data slot in destination register 2120. The indexed data element in table 2 2612 (B1) is stored in a second data slot in destination register 2120. The indexed data element in table 3 2613 (C8) is stored in a third data slot in destination register 2120. The indexed data element in table 4 2614 (D10) is stored in a fourth data slot in destination register 2120. In accordance with this example implementation, other data slots of destination register 2120 are zero filled.

The look up table read instructions maps the data recalled from the table(s) directly to vector lanes of destination register 2120. The instruction maps earlier elements to lower lane numbers and later elements to higher lane numbers. The look up table read instruction deposits elements in vectors in increasing-lane order. The look up table read instruction fills each vector lane of destination register 2120 with elements recalled from the table(s). If the recalled data does not equal the vector length, the look up table read instruction pads the excess lanes of destination register 2120 with zeros.

When a promotion mode is enabled (promotion field 1901 of the corresponding look up table configuration register 1900≠00), the look up table read instruction promotes each recalled data element to a larger size. FIG. 27 illustrates an example of the operation of the look up table read instruction in accordance with an example embodiment. FIG. 27 illustrates an operation similar to FIG. 26 except that a 2× promotion is enabled (promotion field 1901 is 01). As in FIG. 26, each of the four indices of vector source index register 2102 recalls a data element from a corresponding table. FIG. 27 illustrates these are placed in destination register 2120 differently than in FIG. 26. Each recalled data element is stored in a slot in destination register 2120 together with an equally sized extension. This extension is formed corresponding to the signed/unsigned indication of signed field 1904 of the corresponding look up table configuration register. If signed field 1904 indicates unsigned (0), then the extension is zero filled. If signed field 1904 indicates signed (1), then the extension slot is filled with the same value as the most significant bit (sign bit) of the corresponding data element. This treats the data element as a signed integer.

FIG. 28 illustrates an example of the operation of the look up table read instruction in accordance with an example embodiment. FIG. 27 illustrates an operation similar to FIG. 26 except that a 4× promotion is enabled (promotion field 1901 is 10). Each of four indices of vector source index register 2101 recalls a data element from each table. FIG. 2 illustrates these are placed in destination register 2120 differently than in FIG. 21. Each recalled data element is stored in a slot in destination register 2420 together with three equally sized extensions. These extensions are formed corresponding to the signed/unsigned indication of signed field 1904 of the corresponding look up table configuration register.

Those skilled in the art would understand that a data element size of one byte would be similarly implemented. A promotion factor of 8× would be similarly achieved. Those skilled in the art would understand how to apply the principles described in this disclosure to other numbers of look up tables within the selected set of tables.

FIGS. 29A and 29B together illustrate an example embodiment of implementation of promotion. Temporary register 2950 receives table data recalled from level one data cache 123. Temporary register 2950 includes 16 bytes arranged in 16 1-byte blocks lane 1 to lane 16. Note that these lanes are each equal in length to the minimum of data size specifiable in element size field 1905. In this example that is 1 byte/8 bits. Extension elements 2901 to 2908 form the extensions to respective lanes 1 to 8. A plurality of multiplexers 2932 to 2946 couple input lanes from temporary register 2950 to corresponding lanes of destination register 2102. Not all input lanes of temporary register 2950 are coupled to every multiplexer 2932 to 2946. Many multiplexers 2932 to 2946 also receive an extension input and one or more extension elements 2901 to 2908. Note there is no multiplexer supplying lane 1 of output register 2102. Lane 1 of destination register 2102 is always supplied by lane 1 of temporary register 2905 in this illustrated embodiment.

FIG. 30 illustrates an exemplary extension element N of FIG. 29A. The sign bit (S) of data element N of temporary register 2950 supplies one input of a corresponding extension multiplexer 3001. The sign bit of a signed integer is the most significant bit of the value as shown in FIG. 30. A constant 0 supplies a second input of multiplexer 3001. Multiplexer 3001 and other similar multiplexers corresponding to other input data elements are controlled by a signed/unsigned signal. This signed/unsigned signal based upon signed field 1904 of the corresponding look up table configuration register 1900. If signed field 1904 is 0, then multiplexer 3001 (and the corresponding multiplexers for other input lanes) selects the constant 0 input. If signed field 1904 is 1, then multiplexer 3001 (and the corresponding multiplexers for other input lanes) selects the sign bit input. The selected extension is supplied to expansion element 3002. Expansion element 3002 expands the bit selected by multiplexer 3001 to the lane size. In accordance with this example, the lane size is selected to equal the minimum table data element size of 1 byte. For a specified table data size equal to the lane size and in which the signed field 1904 is 0, the next data slot is filled with 0's effecting a zero extension. If signed field 1904 is 1, the next data slot is filled with the sign bit of the data element effecting a sign extension. Multiplexers 2932 to 2946 select the proper extension corresponding to the specified table data element size. If the selected table data element size is half word, multiplexers 2932 to 2946 are controlled to select the extension from alternating extension elements. If the selected table data element size is word, multiplexers 2932 to 2946 are controlled to select the extension from every fourth extension element.

Multiplexers 2932 to 2946 are controlled by multiplexer control encoder 3110 illustrated in FIG. 31. Multiplexer control encoder 3110 receives an element data size input (element size field 1905), a promote indication (promotion field 1901) and generates corresponding control signals for multiplexers 2932 to 2946. Not all input bytes can supply each output byte. Table 10 illustrates this control. Table 10 shows the source data for each of the 16 lanes of destination register 2102 for the various data sizes and promotion modes in accordance with an example embodiment.

TABLE 10 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 --1x 16 15 14 13  12 11  10  9 8 7 6 5 4 3 2 1 b-2x e8  8 e7 7 e6 6 e5 5 e4 4 e3 3 e2 2 e1 1 b-4x e4 e4 e4 4 e3 e3 e3 3 e2 e2 e2 2 e1 e1 e1 1 b-8x e2 e2 e2 e2 e2 e2 e2 2 e1 e1 e1 e1 e1 e1 e1 1 hw-2x e8 e8  8 7 e6 e6 6 5 e4 e4 4 3 e2 e2 2 1 hw-4x e4 e4 e4 e4 e4 e4 4 3 e2 e2 e2 e2 e2 e2 2 1 w-2x e8 e8 e8 e8  8 7 6 5 e4 e4 e4 e4 4 3 2 1 Note that lane 1 of destination register 2102 is always the same as lane 1 of temporary register 2950 regardless of selected data size or promotion factor. The column devoted to lane 1 includes all l's and FIG. 29A illustrates a straight connection between lane 1 of temporary register 2950 and destination register 2102. The first row of Table 10 shows that for no promotion (1×), each lane of destination register 2101 is the same as temporary register 2930 regardless of the selected table data element data size. For a data size of byte and a promotion factor of 2 (b-2×), multiplexer 2932 selects the extension of lane 1 (e1), multiplexer 2933 selects the data of input lane 2, multiplexer 2934 selects the extension of lane 2 (e2), multiplexer 2935 selects the data of input lane 3, multiplexer 2936 selects the extension of lane 3 (e3), etc. For a data size of byte and a promotion factor of (b-4×), multiplexers 2932 to 2934 select the extension of lane 1 (e1), multiplexer 2935 selects the data of input lane 2 and multiplexers 2936 to 2938 select the extension of lane 2 (e2), multiplexer 2939 selects the data of input lane 3, multiplexers 2940 to 2942 select the extension of lane 3 (e3), etc. For a data size of byte and a promotion factor of 8 (b-8×), multiplexers 2932 to 2938 select the extension of lane 1 (e1), multiplexer 2939 selects the data of input lane 2, multiplexers 2940 to 2446 select the extension of lane 2 (e2). For a data size of half word and a promotion factor of 2 (hw-2×), multiplexer 2932 selects the data of lane 2, multiplexers 2933 and 2934 select the extension of lane 2 (e2), multiplexer 2935 selects the data of lane 3, multiplexer 2936 selects the data of lane 4, multiplexers 2937 and 2938 select the extension of lane 4 (e4), etc. For a data size of half word and a promotion factor of 4 (hw-4×), multiplexer 2932 selects the data of lane 2, multiplexers 2933 to 2938 select the extension of lane 2 (e2), multiplexer 2939 selects the data of lane 3, multiplexer 2940 selects the data of lane 4, and multiplexers 2941 and 2946 select the extension of lane 4 (e4). For a data size of word and a promotion factor of 3 (w-2×), multiplexer 2932 selects data of lane 2, multiplexer 2933 selects data of lane 3, multiplexer 2934 selects data of lane 4, multiplexers 2935 to 2938 select the extension of lane 4 (e4), multiplexer 2939 selects the data of lane 5, multiplexer 2940 selects the data of lane 6, multiplexer 2941 selects the data of lane 7, multiplexer 2942 selects the data of lane 8 and multiplexers 2943 to 2946 select the extension of lane 8. As previously described, these are all the combinations of data size and promotion factor supported in the present example.

As will be understood, the various techniques described above and relating to look up table operations are provided herein by way of example only. Accordingly, it should be understood that the present disclosure should not be construed as being limited to only the examples provided above. It should be further appreciated that the various look up table operation techniques disclosed herein may be implemented in any suitable manner, including hardware (suitably configured circuitry), software (e.g., via a computer program including executable code stored on one or more non-transitory tangible computer readable medium), or via using a combination of both hardware and software elements.

While the specific embodiments described above have been shown by way of example, it will be appreciated that many modifications and other embodiments will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing description and the associated drawings. Accordingly, it is understood that various modifications and embodiments are intended to be included within the scope of the appended claims. 

What is claimed is:
 1. A digital data processor comprising: an instruction memory storing instructions each specifying a data processing operation and at least one data operand field; an instruction decoder connected to the instruction memory for sequentially recalling instructions from the instruction memory and determining the data processing operation and the at least one data operand; and at least one operational unit connected to a data register file and to an instruction decoder to perform a data processing operation upon at least one operand corresponding to an instruction decoded by the instruction decoder and storing results of the data processing operation, wherein the at least one operational unit is configured to perform a table recall in response to a look up table read instruction by: recalling data elements from a specified location in a specified number of at least one table, the recalled data elements having a specified data size; and storing the recalled data elements in successive slots in a destination register, wherein each recalled data element is promoted to be stored in the destination register in a larger data size than the specified data size.
 2. The digital data processor of claim 1, wherein: the data register file includes a plurality of data registers designated by register number, each data register storing data; the look up table read instruction includes a destination operand field specifying a register number of one of the data registers in the data register file; and the instruction decoder is configured to decode the look up table read instruction to identify the data register having the register number of the destination operand field as the destination register.
 3. The digital data processor of claim 2, wherein the instruction decoder is configured to decode the look up table read instruction to employ portions of a source operand stored in the data register corresponding to the specified register number as a pointer to the specified location of the recall.
 4. The digital data processor of claim 3, wherein: the look up table read instruction specifies a look up table base address register storing a table base address; and the instruction decoder is configured to decode the look up table read instruction to employ the pointer as an offset to the table base address stored in the look up table base address register.
 5. The digital data processor of claim 1, wherein the look up table read instruction specifies a look up table configuration register having a look up table data element size field that indicates the specified data size.
 6. The digital data processor of claim 5, wherein the look up table configuration register includes a promotion field specifying a promotion factor between the specified data size and the larger data size.
 7. The digital data processor of claim 6, wherein the promotion field is configured to indicate a promotion factor selected from one of no promotion, 2× promotion, 4× promotion and 8× promotion.
 8. The digital data processor of claim 5, wherein: the look up table configuration register includes a sign field designating unsigned or signed; the at least one operational unit, in response to the look up table read instruction, is configured to store extension bits in the destination register as 0 when the sign field designates unsigned and as the most significant bit of the recalled data element when the sign field designates signed; and the number of extension bits being equal to the difference between the larger data size and the specified data size.
 9. The digital data processor of claim 5, wherein the look up table configuration register includes a table size field specifying a size of each of the at least one table.
 10. The digital data processor of claim 5, wherein the look up table configuration register includes a field specifying a number of tables of a table set.
 11. The digital data processor of claim 1, further comprising: a level one data memory comprising: a first portion including a level one data cache connected to the at least one operational unit, wherein the first portion is configured to store data for manipulation by the at least one operational unit, wherein the level one data cache services memory reads and writes of the least one operational unit; and a second portion including memory directly accessible via the at least one operational unit, wherein the at least one table is stored in the second portion of the level one data memory; wherein a location from which the data elements are recalled by the at least one operational unit in response to the look up table read instruction are in the second portion of the level one data memory. 